you could ask amazon how to quickly download all books to a fresh install of kindle for PC. if they can solve that step for you. it iis just a couple of clicks to trigger the process of copying them from my documents into calibre library.
i just looked at my modest Kindle library in K for PC but here is no obvious way to select more than one book for download. SHIFT + select, CTRL+A do not seem to work
possibly you can talk Amazon tech/customer support into pushing all 17000 to your PC, as a one-off or maybe you can do it via the manage my content and devices web pages
I would strongly recommend leaving calibre out of any discussion with amazon, just focus on getting all of your library downloaded to a Kindle for PC, because the rest is v easy.
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